UNIVERSITY    OF    CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 


PRUNING  BEARING  DECIDUOUS 
FRUIT  TREES 


BY 
WARREN  P.  TUFTS 


BULLETIN  No.  386 

April,  1925 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 
BERKELEY,  CALIFORNIA 
1925 


PRUNING  BEARING  DECIDUOUS  FRUIT  TREES 

By  WAEREN  P.  TUFTS 


Pruning  consists  of  cutting,  removing  or  repressing  certain  living 
parts  of  the  tree  in  order  to  modify  and  utilize  its  natural  habits  for 
the  purposes  of  the  grower.  By  pruning,  the  form  of  the  tree  is 
modified,  its  bearing  regulated  and  thereby  more  and  better  fruit  is 
obtained  at  less  cost  and  for  a  longer  period  than  is  possible  without 
pruning.  The  response  of  a  tree  to  any  kind  of  pruning  is  such,  how- 
ever, that  it  is  practically  impossible  to  modify  its  form  without  at 
the  same  time  profoundly  influencing  its  functions.  There  must  be 
understood  the  various  operations  of  pruning  and  how  to  apply  these 
operations  to  obtain  the  responses  which  are  necessary. 

Briefly  stated,  the  chief  purposes  of  pruning  are : 

1.  To  produce  a  vigorous,  mechanically  strong,  healthy  tree. 

2.  To  secure  a  tree  well  shaped  for  convenience  and  economy  in 
orchard  management. 

3.  To  distribute  the  fruiting  area  well  over  the  tree. 

4.  To  secure  fruit  of  good  size  and  quality. 

5.  To  regulate  the  annual  succession  of  crops  in  order  to  obtain  the 
maximum  average  crop  compatible  with  good  fruit. 

The  principles  and  practices  of  pruning  young  deciduous  fruit 
trees  have  been  discussed  in  a  previous  publication.1  The  present 
discussion  will  be  limited  largely  to  a  consideration  of  the  pruning  of 
bearing  trees. 

TERMS  USED 

Leaf-bud. — A  leaf -bud  contains  the  rudiments  of  a  leafy  shoot  or 
spur. 

Fruit-bud. — A  fruit-bud  contains  the  rudiments  or  unexpanded 
parts  of  a  flower  or  flowers,  with  or  without  the  rudiments  of  a  leafy 
shoot. 

Adventitious  buds. — All  buds  arising  in  unusual  or  abnormal 
places,  whether  on  parts  below  or  above  ground,  are  called  "adventi- 
tious buds. ' '  The  usual  position  for  all  buds;  of  course,  is  in  the  leaf 
axils  (angles  formed  by  leaf  stalks  and  one-year  wood)  or  at  the  tip 
of  the  shoots. 


i  Tufts,  W.  P.     Pruning  young  deciduous  fruit  trees.     California  Exp.  Sta. 
Bull.  313:  311-154,  figs.  1-24.     1919. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Suckers  and  Water-Sprouts. — All  growth  arising  from  adventitious 
buds  on  the  parts  below  ground  are  called  ' '  suckers, ' '  that  arising  from 
such  buds  on  above  ground  parts  and  from  dormant  axillary  buds 
"  water-sprouts. " 


Fig.  l.- 


-Fruit-bud  of  the  peach.     Note  the  two  lateral  fruit-buds  with  a 
small  leaf -bud  between. 


Spurs. — Many  species  of  fruit  trees  produce  short  shoots  which 
bear  flowers  and  fruit,  and  are  called  ' '  spurs. ' ' 

Current  and  One-Year  Growth. — Any  new  shoot  is  referred  to 
during  the  growing  season  as  "current"  or  "this  year's"  growth. 
This  same  shoot,  however,  during  the  following  dormant  and  growing 
seasons,  is  referred  to  as  "  one-year ' '  wood.  In  the  same  way,  reference 
is  made  to  "two-year-old"  wood,  etc. 


Bulletin  386]      pruning  bearing  deciduous  fruit  trees 


FEUIT  BEARING  HABITS 

In  order  to  prune  fruit  trees  intelligently,  it  is  necessary  to  have  a 
thorough  understanding  of  the  various  kinds  of  buds  and  of  their 
relation  to  the  fruit  bearing  habits  in  the  different  species  and  varieties. 
The  following  classification  is  based  on  the  location  and  external 
appearance  of  leaf-  and  fruit-buds. 

Classification  of  Buds. — As  to  development,  the  kinds  of  buds  are : 

1.  Wood-  or  leaf -buds,  which  develop  into  leafy  shoots. 

2.  Fruit-buds,  which  are  of  two  kinds : 

(a)  Flower-buds,  which  develop  into  a  single  flower  (peaches, 
apricots,  almonds)  or  several  flowers  (cherries,  plums). 

(&)   Mixed  buds,  which  develop  into  a  cluster  of  leaves  and 
flowers  (apples,  pears). 
As  to  position,  the  kind  of  buds  are : 

1.  Lateral  buds,  which  are  in  the  axils  of  leaves  on  the  sides  of  the 
shoots. 

2.  Terminal  buds,  which  are  on  the  ends  of  shoots. 

3.  Adventitious  buds,  which  are  produced  at  unusual  points  (not 
leaf  axils),  on  the  roots,  trunk,  or  branches. 

Recognition  of  Fruit-Buds: 

The  positions  of  fruit-buds  are : 

1.  On  comparatively  long  shoots  of  the  past  season  one-year  wood. 

(a)  Lateral  (fig.  1).  In  this  position  are  found  almost  all  the 
fruit-buds  of  the  grape,  peach,  quince,  and  olive,  many  of 
the  fruit-buds  of  currants  and  gooseberries,  part  of  those  of 
apricots,  almonds,  plums,  cherries,  and  sometimes  pears, 
apples,  and  walnuts ;  and  the  fruit-buds  for  the  first  crop  of 
figs.  Apricots,  peaches,  and  Japanese  plums  often  bear 
three  buds  at  a  node,  in  which  case  the  center  one  is  usually 
a  leaf -bud,  and  the  two  outer  ones  fruit-buds. 

(b)  Terminal.  This  is  the  normal  position  of  most  of  the  fruit- 
buds  of  the  walnut.  Some  varieties  of  apples  and  pears  also 
frequently  bear  a  considerable  number  of  fruit-buds  in  this 
way. 

2.  On  comparatively  short  shoots  (spurs)  of  the  past  season. 
(These  short  shoots  constitute  either  an  extension  of  the  spur  system 
already  established  or  the  beginning  of  a  new  spur.) 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  2. — Apricot  fruit-spurs.  Scars  where  fruit  has  been  produced  at  X. 
Fruit-buds  at  Y.  Leaf-buds  at  Z.  Two-year-old  spur  at  A.  One-year-old 
spur  at  B. 


BULLETIN  38G]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES 


Fig.  3. — Fruit-spurs  of  plums.  Left  to  right:  Robe  de  Sargent  (European); 
Wickson  (Japanese);  Yellow  Egg  (European).  Note  small  roundish  fruit-buds 
of  the  Wickson  which  are  characteristic  of  Japanese  plums.  The  Robe  de 
Sargent  has  a  more  compact  spur  system  than  most  European  plums. 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

(a)  On  short-lived  spurs,  which  may  live  only  3  years  or  less 

(%  2). 
(1)  Lateral  buds.  Most  of  the  fruit-buds  of  apricots  and 
almonds  are  in  this  position.  Peaches  occasionally  bear 
a  small  part  of  their  fruit-buds  in  this  manner.  All  the 
fruit-buds  of  currants  and  gooseberries  on  shoots  older 
than  one  year  are  borne  in  this  way. 

(b)  On  medium-lived  spurs  which  may  live  5  to  8  years  (fig.  3). 

Plums  bear  most  of  their  fruit-buds  laterally  in  this  way. 


Fig.  4. — Three-year-old  portion  of  a  pear  spur.  Note  terminal  fruit-bud  at 
A,  and  two  lateral  leaf -buds  at  B.  Fruit  was  produced  at  C  during  season  pre- 
ceding that  in  which  buds  A  and  B  were  formed.  Growth  of  "B"  buds  will 
give  rise  to  characteristic  branching  of  older  pear  spurs. 


Bulletin  386]      pruning  bearing  deciduous  fruit  trees  9 

(c)   On  long-lived  spurs  which  live  10  to  20  years,  but  which 
should  be  renewed  (or  at  least  invigorated)  oftener. 

(1)  Lateral  buds.     Most  fruit-buds  of  sweet  cherries  and 
part  of  those  of  sour  cherries  are  borne  in  this  way. 

(2)  Terminal  buds  (fig.  4).    Most  of  the  fruit-buds  of  the 
apple  and  pear  are  terminal. 

The  Appearance  of  Fruit-Buds. 

The  fruit-buds  of  the  apple,  pear,  peach,  apricot,  and  plum  are 
larger  and  plumper  and  are  not  so  sharply  pointed  as  the  wood-buds. 
Cherry  fruit-buds  are  difficult  to  distinguish  until  they  begin  to  swell. 
The  most  certain  way  of  determining  fruit-buds  is  by  sectioning  the 
bud  lengthwise  with  a  sharp  knife  or  razor.  The  fruit-buds  of  the 
apple,  pear,  cherry,  and  plum  contain  several  roundish  bodies,  each  of 
which  develops  into  a  flower.  The  fruit-buds  of  the  almond,  peach, 
and  apricot  each  contains  the  rudiments  of  a  single  flower.  A  pocket 
magnifying  glass  is  of  considerable  help  in  this  examination. 

The  following  chart  presents  the  above  facts  in  a  somewhat  more 
concise  manner: 

Positions  of  Fruit-Buds  of  Deciduous  Fruits 


Spurs  (Short  Shoots) 


T,  a, 
o  o 

o 

'c? 


Terminal 
Apple 
Pear 


T,  a, 
o  o 

o 


Spurs  and  Long  Shoots 
Lateral 
Almond 
Apricot 
Sour  Cherry- 
Japanese  Plum 
Currant 
Gooseberry 


Long  Shoots 
Lateral 
Peach 
Olive 
Quince 
Grape 
Fig 

Loganberry 
Raspberry 

Terminal 
Walnut 


Lateral 

Sweet  Cherry 
European  Plum 
and  Prune 

Lateral 

Peach  (spurs 
short-lived) 


Lateral 

Sweet  Cherry 
European  Plum 

and  Prune 
Quince 
Walnut 

Lateral  and  Terminal 
Apple 
Pear 


10  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

THE  SOURCE  OF  MATERIALS  FOR  TREE  AND  CROP 

In  order  to  comprehend  the  responses  of  the  plant  to  pruning, 
certain  facts  should  be  known  concerning  the  annual  cycle  of  growth 
and  development  of  the  tree.  The  first  growth  of  the  season  (blossoms, 
leaves,  and  new  shoots)  is  made  largely  at  the  expense  of  plant  food 
reserves  normally  stored  in  the  tree  during  the  preceding  summer  and 
fall.  These  stored  foods  are  thus  at  least  partially  used  up  during  the 
early  part  of  the  summer.  The  soil  solution  containing  mineral 
nutrients  taken  up  by  the  roots  is  transported  to  the  leaves  where,  with 
other  substances  built  from  the  carbon  dioxide  of  the  air,  the  complex 
plant  foods  are  elaborated.  These  foods  are  then  carried  to  other  parts 
of  the  tree  for  use  or  storage.  After  the  active  vegetative  period  of 
early  summer  is  past,  the  plant  begins  to  store  such  elaborated  foods 
as  are  not  used  in  the  maturing  of  the  current  fruit  crop,  development 
of  leaves,  the  extension  of  the  top  and  roots,  and  the  development  of 
fruit-buds  for  the  succeeding  year's  crop.  Under  favorable  conditions, 
the  storage  of  reserves  for  the  winter  months  and  for  the  growth  of  the 
following  year  becomes  greater  and  greater  as  the  season  advances,  at 
least  until  near  the  time  of  leaf  fall. 

A  fruit  tree  with  the  crops  it  produces  represent  an  accumulation 
of  materials  drawn  from  the  soil  by  the  roots  and  from  the  air  by  the 
leaves.  When  the  materials  from  either  source  can  no  longer  be 
obtained,  it  ceases  to  exist  as  a  living  thing.  Since  this  is  so,  any  plan 
of  developing  and  managing  an  orchard  from  the  time  it  is  planted  to 
the  time  it  is  no  longer  profitable,  must  take  into  consideration  the 
treatment  of  the  soil,  and  the  treatment  of  the  top,  especially  pruning. 
Trees  develop  or  produce  very  differently  in  different  locations,  and 
respond  rather  readily  to  cultural  practices.  This  being  true,  it  is 
necessary  to  know  what  influence  a  change  in  the  quantities  and  kinds 
of  material  available  in  the  soil  may  have  on  the  appearance  and 
behavior  of  the  top,  especially  in  relation  to  materials  already  in  the 
top,  or  to  those  being  brought  in  by  the  leaves.  Or  from  the  other 
point  of  view — just  what  influence  pruning,  spraying,  insect  infesta- 
tion, or  any  other  factor  may  exert  in  changing  the  material  income 
of  the  top,  and  its  relation  to  the  materials  derived  from  the  soil,  and 
the  subsequent  development  of  the  top  ?  Only  by  such  a  consideration 
of  orchard  problems  can  they  finally  be  worked  out  with  certainty. 
The  full  so" ill  'on  of  this  problem  will  require  time  and  labor,  but  some 
progress  has  b^en  made,  and  it  seems  possible  to  give  the  orchardist  a 
working  insight  into  the  problem  at  the  present  time,  and  to  offer 
suggestions,  as  to  the  character  of  pruning  and  of  the  supplementary 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  11 

soil  treatments  that  should  be  applied  under  varying  conditions  of 
growth  and  bearing.  There  is  much  observational  evidence  and  no 
small  amount  of  direct  experimentation  to  show  that  plants  respond 
very  differently  in  growth  and  fruit  production,  according  to  the 
amounts  of  nitrogen  available,  the  amounts  of  carbohydrates  that  can 
be  manufactured,  and  the  manner  in  which  these  are  combined  within 
the  plant.  Very  great  differences  likewise  may  be  brought  about  by 
variations  in  temperature  and  the  length  of  the  light  period  to  which 
plants  are  exposed.  Plants  growing  out-of-doors,  supplied  with  suffi- 
cient moisture  and  subjected  to  the  usual  range  of  conditions  will  vary 
in  development  and  productivity  according  to  the  amounts  of  nitro- 
genous materials  available  in  the  soil  and  to  the  amounts  of  available 
carbohydrates  manufactured  by  the  leaves  or  stored  in  the  plants. 

It  is  possible  to  distinguish  four  general  classes  or  states  of  vegeta- 
tiveness  and  fruitfulness  of  the  plant  in  this  respect. 

1.  Mineral  nutrients  including  nitrates  abundant  but  no  available 
carbohydrate  supply.  Result :  vegetativeness  weak  and  plants  non- 
fruitful. 

2.  Mineral  nutrients  including  nitrates  abundant  and  a  carbo- 
hydrate supply  available.  Result :  vegetativeness  strong  but  little  or 
no  fruit. 

3.  Mineral  nutrients  including  nitrates  relatively  less  than  in  class 
2.  This  reduces  vegetativeness  and  leads  to  an  accumulation  of  carbo- 
hydrates.    Result :    fruitfulness. 

4.  Mineral  nutrients  including  nitrites  even  relatively  less  than  in 
class  3.  Result :  this  leads  to  a  marked  accumulation  of  carbohydrates 
and  a  suppression  of  both  vegetativeness  and  fruitfulness.2 

Naturally  these  classes  grade  into  one  another,  but  it  is  possible  to 
place  trees  in  one  or  another  of  them  with  a  considerable  degree  of 
accuracy,  by  observing  the  appearance  and  performance  of  the  trees 
and  knowing  the  general  cultural  conditions  which  have  been  employed. 
For  the  fruit  grower,  it  is  obviously  impracticable  to  attempt  an  actual 
analysis  of  the  trees  in  an  orchard  to  determine  their  chemical  content 
and  therefore  the  treatment  as  to  pruning,  irrigation,  fertilization, 
and  other  cultural  practices,  which  should  be  given.  But,  as  indicated 
above,  the  crops  produced  and  the  new  wood  growth  made,  generally 
furnish  an  excellent  basis  for  judgment  and  a  fairly  accurate  decision 
as  to  what  is  happening  in  the  plant.  The  author  has  attempted  to 
cite  below  some  points  to  be  kept  in  mind  in  connection  with  the  fore- 
going suggestions  and  instances  in  which  fruit  trees  apparently  fall 
in  one  or  another  of  the  above  outlined  classes. 


2  Kraus  and  Kraybill.     Vegetation  and  reproduction  with  special  reference 
to  the  tomato.     Ore.  Exp.  Sta.  Bull.  149:  1-90,  tigs.  1-22.     1918. 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

It  has  been  demonstrated  many  times  that  heavy  cutting,  whether 
done  on  young  trees  or  old,  generally  results  in  rank  vegetative  growth, 
and,  if  the  trees  are  of  bearing  age,  in  reduction  of  f ruitfulness.  How- 
ever, if  in  addition  to  the  pruning,  the  trees  are  heavily  fertilized  and 
irrigated,  the  new  growth  will  be  still  ranker  and  more  succulent,  and 
little  or  no  fruit  will  be  produced.  On  the  other  hand,  no  pruning, 
insufficient  soil  moisture  and  few  available  mineral  nutrients  will 
result  in  scanty  new  wood  growth  and,  in  bearing  trees,  a  tendency 
towards  over-production.  If  this  latter  treatment  is  continued  trees 
soon  reach  a  condition  where  there  is  neither  wood  nor  fruit  produced. 
Between  these  extremes  may  be  found  all  gradations  of  vegetativeness 
and  reproductiveness,  depending  upon  the  environment  under  which 
the  plants  are  growing. 

Fruit  growers  will  readily  call  to  mind  orchards  exhibiting  varying 
degrees  of  vegetative  vigor  and  fruitfulness.  Unfortunately,  many 
attempts  in  the  past  have  been  made  to  influence  the  wood  growth  and 
the  productiveness  of  the  tree  by  pruning  alone.  This  is  a  mistake, 
since  pruning  is  only  one  of  the  factors  which  modify  plant  growth 
and  productiveness. 

Cultivation,  irrigation,  and  application  of  fertilizers  are  some  of 
the  other  factors  which  must  be  considered  along  with  pruning  in 
attempting  to  regulate  the  vegetative  growth  and  fruitfulness  of  an 
orchard. 

Trees  just  planted  have  relatively  little  carbohydrate,  but  enough 
to  start  them  into  growth.  As  they  develop,  leaves  are  formed  which 
manufacture  a  new  supply  of  carbohydrates;  and  as  the  leaf  area 
becomes  greater  this  supply  is  increased,  the  roots  are  extended  further 
into  the  soil,  and  the  tree  becomes  vigorously  vegetative,  that  is,  it 
belongs  to  class  2. 

If,  however,  such  young  trees,  or  even  older  ones,  are  severely 
summer  pruned  so  that  the  leaf  area  is  seriously  reduced,  the  food 
stored  in  the  branches  will  be  consequently  removed,  and  the  tree  as  a 
whole  will  fail  to  make  as  much  growth  as  one  less  severely  pruned, 
other  conditions  being  the  same.  This  would  represent  a  class  1 
condition. 

On  the  other  hand,  if  the  young  vigorous  trees  are  not  so  severely 
cut  back,  the  consequent  larger  leaf  area  will  permit  of  a  greater 
manufacture  of  carbohydrates,  and  provided  the  nitrogen  supply  is 
not  markedly  increased,  there  will  be  a  tendency  toward  a  decrease  of 
vegetative  activities,  an  increase  in  carbohydrate  accumulation  and 
the  trees  will  become  fruitful.  Such  plants  are  in  class  3.  It  is  the 
ultimate  aim  of  every  commercial  orchardist,  to  maintain  his  trees  in 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  13 

this  class  and  his  main  efforts  in  the  way  of  cultivation,  irrigation, 
pruning,  and  other  cultural  practices  should  be  performed  with  the 
idea  of  securing  a  proper  balance  between  vegetative  growth  and 
fruitfulness.  The  production  of  a  large  number  of  fruits  is  not 
profitable,  unless  it  can  be  continued  and  for  this  a  constant  supply 
of  new  growth  must  be  maintained  as  well.  By  knowing  some  of  the 
materials  concerned  in  the  maintenance  of  this  condition,  and  some  of 
the  means  for  their  regulation,  the  fruit  grower  has  a  direct  and  fairly 
accurate  method  for  securing  the  type  of  tree  he  desires. 

The  conditions  of  class  4  are  commonly  observed  in  old  prune  and 
pear  orchards  in  California,  which  make  little  or  no  new  growth  and, 
although  there  is  present  a  great  number  of  fruit-spurs,  little  or  no 
fruit  is  produced.  In  these  cases  the  difficulty  is  frequently  one  of 
lack  of  nitrogen,  because  there  is  an  accumulation  of  large  quantities 
of  carbohydrates  stored  in  the  top.  Such  trees  as  these  when  nitrogen 
and  moisture  are  supplied,  or  if  there  is  available  nitrogen  already  in 
the  soil,  when  moisture  alone  is  applied,  frequently  are  unusually 
productive  for  a  year  or  two.  Likewise,  a  pruning  which  removes 
much  of  the  old  wood  and  permits  a  relatively  greater  nitrogen  supply 
to  the  branches  and  buds  remaining  results  in  a  greatly  increased 
vegetativeness  of  the  remaining  portions,  often  accompanied  by  abun- 
dant fruit  production  as  well.  But  to  attempt  to  regulate  such  trees 
by  pruning  alone  would  be  futile,  because  to  balance  the  top  with  the 
available  nitrogen  or  moisture,  would  mean  reducing  the  top  to  a  size 
where  it  could  hardly  produce  a  commercial  crop.  It  would  be  far 
more  profitable  to  give  the  proper  attention  to  soil  requirements,  as 
well  as  to  a  more  rational  pruning  method. 


CORRELATION  BETWEEN  PRUNING  AND  OTHER  CULTURAL 

PRACTICES 

The  above  considerations  emphasize  the  fact  that  pruning  alone 
cannot  be  relied  upon  to  regulate  the  growth  and  productivity  of  the 
orchard.  It  is  doubtless  one  of  the  most  important  factors  in  deter- 
mining the  balance  between  carbohydrate  and  nitrogen  supply,  but  a 
thorough  understanding  of  the  principles  involved  must  be  obtained 
before  a  rational  pruning  system  can  be  adopted  for  any  particular 
set  of  conditions. 

There  may  be  an  adequate  supply  of  available  nitrogen,  but  if  soil 
moisture  is  reduced  to  such  an  extent  that  the  tree  cannot  utilize  this 
food  material,  then  the  pruning  must  be  such  that  a  proper  balance 
will  be  maintained.     Pruning  under  such  circumstances  should  prob- 


14 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


ably  be  considerably  heavier  in  order  to  reduce  the  amount  of  water 
lost  through  evaporation,  and  to  maintain  a  relatively  higher  propor- 
tion of  nitrogen  to  the  carbohydrates  present  or  being  manufactured, 
than  if  there  were  available  an  adequate  supply  of  soil  moisture  and 
nitrogen. 

In  the  same  way,  cultivation,  irrigation,  and  fertilizers  affect  the 
pruning  practice  by  limiting  or  increasing  the  amounts  of  soil  moisture 
and  available  minerals,  especially  nitrogenous  compounds. 


NEW  WOOD  NECESSARY  FOR  FUTURE  FRUITFULNESS 

As  previously  suggested,  the  amount  and  character  of  the  new  wood 
produced  during  any  season  may  be  taken  as  an  index  of  the  condi- 
tions existing  within  the  tree.  The  amount  of  new  vegetation  neces- 
sary to  maintain  the  correct  balance  apparently  differs  with  the  species 
in  question.  In  general,  it  may  be  said  that  those  fruits,  such  as  the 
peach,  which  bear  the  bulk  of  their  crop  on  one-year  wood,  associate 
fruitfulness  and  a  relatively  greater  amount  of  new  growth  than  seems 
necessary  with  spur  producers.  In  the  case  of  spur  producers,  those 
species  which  have  the  longest  lived  spurs  apparently  need  the  least 
amount  of  new  wood.  This  seems  reasonable,  since  at  least  a  portion 
of  such  new  growth  must  be.  used  for  replacement  of  fruit-wood  which 
has  outlived  its  usefulness.  The  amount  of  new  growth  necessary  for 
continued  fruitfulness  may  vary  from  a  few  inches,  in  the  case  of 
such  fruits  as  the  apple  and  pear,  to  from  two  to  four  feet  in  the  case 
of  the  peach. 

TABLE  1 

Desirable  Amounts  of  New  Growth  for  Bearing  Trees 


Fruits 

Peaches 

Apricots 

Plums  (excepting  prunes)  and  Quinces 

Almonds,  prunes,  apples,  pears,  cherries 


Under  10  years  of  age 


Over  10  years  of  age 


20  to  40  inches 

12  to  30  inches 

10  to  24  inches 

9  to  18  inches 


12  to  30  inches 

10  to  24  inches 

9  to  18  inches 

6  to  10  inches 


BULK  VERSUS  FINE  PRUNING 

The  question  may  well  be  asked  whether  or  not  pruning  should 
consist  in  a  few  large  or  many  small  cuts  distributed  well  over  the 
tree.  Horticulturists  are  generally  of  the  opinion  that  the  immediate 
influence  of  a  pruning  cut  does  not  extend  far  from  the  place  it  is 
made  and  that,  therefore,  it  is  desirable  to  distribute  the  pruning 


Bulletin  386]       pruning  BEARING  DECIDUOUS  FRUIT  TREES  15 

over  as  large  a  portion  of  the  tree  as  is  economically  possible.  (Of 
course  the  total  amount  of  cutting  done  does  eventually  produce  an 
influence  throughout  the  tree  as  a  whole.)  Whether  the  cuts  should 
average  one-fourth  inch,  one-half,  or  one  inch  in  diameter,  very  largely 
depends  upon  the  species  under  consideration.  In  the  case  of  the 
peach,  where  the  bulk  of  the  fruit  wood  must  be  renewed  annually, 
many  cuts  must  be  made  in  order  to  secure  a  large  number  of  new 
shoots  well  distributed.  With  those  species  producing  on  spurs,  how- 
ever, a  comparatively  few  cuts  may  often  suffice. 

Bulk  pruning  by  the  removal  of  relatively  large  limbs  commonly 
gives  rise  to  numerous  water-sprouts.  These  may  at  times  be  utilized 
in  rebuilding  the  framework  of  the  tree  and  a  few  of  them,  under 
favorable  conditions,  may  be  converted  into  a  part  of  the  fruit-spur 
system.  Generally  speaking,  however,  these  growths  are  of  little  value 
and  should  be  removed  entirely  as  soon  as  they  appear. 

SPUR  PRUNING 

Spur  pruning  is  essentially  "fine"  pruning  and  is  often  utilized 
in  the  rejuvenation  of  orchards  which,  for  one  reason  or  another,  have 
fallen  into  class  4  (page  11).  It  consists  in  the  removal  of  whole 
spurs  or  of  portions  of  spurs,  and  tends  to  stimulate  vegetative  growth. 
On  account  of  the  labor  cost  involved  and  the  fact  that  most  trees  are 
very  "brushy,"  comparable  results  are  usually  secured  by  a  somewhat 
"coarser"  method  of  cutting. 

TRANSITION  FROM  NON-BEARING  TO  BEARING 

The  lighter  the  pruning  of  young  trees,  consistent  with  the  securing 
of  a  proper  framework  of  scaffold  branches,  the  greater  will  be  their 
development  and  the  sooner  profitable  crops  will  be  produced.  The 
more  severely  young  trees  are  pruned,  the  longer  they  remain  unfruit- 
ful. Continued  heavy  cutting  not  only  reduces  the  chances  for  a 
fruit  crop,  especially  with  spur  producers,  and  very  materially  reduces 
wood  development  (fig.  5  and  fig.  6),  but  it  also  tends  to  move  such 
trees  from  class  2  into  class  1. 

It  is  a  matter  of  common  experience  that  with  fruit  trees  which 
are  just  beginning  good  production,  it  is  possible  by  injudicious  heavy 
cutting  during  one  season  so  to  disturb  the  delicate  balance  between 
wood  growth  and  fruiting  that  profitable  cropping  is  delayed  as  much 
as  three  or  four  years.  The  best  judgment  must  always  be  exercised 
when  determining  the  pruning  treatment  to  be  given  any  particular 
orchard;  this  is  especially  true  when  the  trees  are  just  approaching 
the  bearing  age. 


16 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


As  the  trees  become  older  and  bearing  is  fully  established,  many 
instances  will  doubtless  arise  in  which  heavier  pruning  will  be  neces- 
sary in  order  to  continue  regular  bearing  and  to  maintain  the  necessary 
wood  growth  at  the  same  time.  To  this  end  supplementary  fertilization 
may  be  advisable  or  even  necessary. 


Fig.  5. — Five-year-old  Nonpareil  almond  tree  after  pruning.  This  tree  has 
been  lightly  pruned  each  year.  Compare  figure  6  of  an  adjoining  tree  which 
has  been  severely  pruned  annually.  Note  relative  sizes  of  trees  and  branches. 
Photographed  at  same  distance  as  tree  shown  in  fig.  6.  With  the  exception  of 
the  pruning,  these  trees  have  received  identical  treatment.  This  tree  is  a 
representative  specimen  of  a  large  number  of  trees  similarly  treated. 


PEOMOTION  OF  FEUITFULNESS 

Distribution  of  Fruiting  Wood. — Pruning  is  of  value  in  distribut- 
ing fruiting  wood  uniformly  jthroughout  the  tree,  thus  securing  greater 
tonnage  of  better  quality.  By  this  means,  the  trees  are  kept  within 
bounds  and  the  costs  of  maintenance  and  harvesting  are  reduced. 

Fruit-Bud  Formation. — Sufficient  light  in  all  fruit  producing  parts 
of  the  tree  is  essential  in  order  to  secure  a  uniform  distribution  of 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  17 

fruit-buds.    Pruning  is  practically  the  only  means  of  securing  favor- 
able light  distribution.     (See  also  page  18.) 

Although  fruit-buds  for  any  crop  begin  their  development  the 
previous  summer  (June  to  August,  under  practically  all  California 
conditions),  nevertheless,  the  pruning  of  bearing  trees  at  that  time  is 
of  doubtful  value  as  a  means  of  securing  greater  fruitfulness.  This 
point  will  be  discussed  later  in  more  detail  (page  18). 


Fig.  6. — Five-year-old  Nonpareil  almond  tree  after  pruning.  This  tree  has 
been  heavily  pruned  each  year.  Compare  fig.  5  of  an  adjoining  tree  lightly 
pruned.  Note  relative  sizes  of  trees  and  branches.  Photographed  at  same 
distance  as  tree  shown  in  fig.  5.  This  tree  is  a  representative  specimen  of  a 
large  number  of  trees  similarly  treated. 

Regular  Pruning. — Optimum  results  are  obtained  only  when  the 
pruning  treatment  is  consistently  and  regularly  carried  out  over  a 
period  of  years.  It  is  possible  with  some  species  to  allow  the  trees  to 
remain  unpruned  for  several  years,  but  the  net  returns  from ,  such 
treatment  are  smaller  than  those  secured  from  annual  cutting  which 
insures  a  constant  renewal  of  fruiting  wood.  Pruning  should  be  part 
of  each  season's  operations  even  though  the  amount  of  wood  removed 
in  some  instances  may  be  comparatively  small. 

New  Wood  and  Size  of  Fruit. — There  is  apparently  a  direct  cor- 
relation between  new  vegetative  growth  and  size  of  fruit.  Trees  which 
make  a  satisfactory  wood  growth  usually  bring  the  fruit  crop  through 
with  larger  sizes  than  do  those  which  are  unsatisfactory  in  this  respect. 
It  is  the  common  experience  of  fruit  growers  that  relatively  young, 
vigorously  growing  trees  nearly  always  produce  fruit  of  large  size. 


18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

EEGULATION  OF  SIZE  AND  QUALITY  OF  THE  FEUIT  CEOP 

Fruit  trees  normally  tend  to  produce  more  fruit  than  can  be  suc- 
cessfully carried  through  to  maturity,  hence,  it  has  become  an  estab- 
lished orchard  practice  to  reduce  this  burden  somewhat  at  the  annual 
dormant  pruning.  On  account  of  certain  fruiting  habits,  danger  from 
spring  frosts,  liability  to  the  "June  drop,"  and  other  factors  which 
may  decrease  the  final  crop,  it  is  not  feasible  to  attempt  to  do  all  the 
thinning  of  fruit  with  the  pruning  shears.  In  order  to  reduce  by  any 
pruning  system  the  number  of  fruits  set  so  that  there  will  exist  no 
necessity  for  hand-thinning,  it  is  necessary  to  limit  the  crop  pro- 
duced to  less  than  that  which  the  trees  can  successfully  mature. 
Such  severe  pruning  as  this  requires,  will  moreover  be  inimical  to 
future  productivity. 

Color  of  fruit  is  one  of  those  characteristics  difficult  to  define,  which 
with  size,  finish,  and  flavor,  constitute  "quality."  Light  is  of  prime 
importance  in  securing  color,  but  if  the  tree  is  rightly  "opened  up" 
by  pruning,  little  difficulty  will  be  experienced  in  this  connection.  In 
attempting  to  secure  good  color  by  allowing  light  to  penetrate  to  the 
interior  of  the  tree,  care  must  be  exercised  that  the  scaffold  branches 
are  not  exposed  to  the  direct  rays  of  the  sun,  as  this  would  result  in 
sunburn  and  in  subsequent  decay  of  the  wood.  Likewise,  the  new 
growth  must  be  sufficient  to  shade  the  fruit  and  protect  it  from 
sunburn,  especially  in  the  dry,  hot  interior  valleys. 

WHEN  TO   PRUNE 

The  old  axioms  of  "prune  when  the  knife  is  sharp,"  and  "summer 
prune  for  fruit  and  winter  prune  for  wood,"  are  an  unsafe  guide 
and  the  fruit  grower  should  have  a  more  reasonable  basis  for  his 
pruning  practice. 

The  general  statement  may  be  made  that  for  all  deciduous  orchards 
in  California,  pruning  gives  the  best  results  when  done  during  the 
dormant  season,  after  leaf-fall  and  before  new  growth  starts  the 
following  spring. 

It  has  frequently  been  argued  that  to  increase  fruitfulness,  trees 
should  be  pruned  in  the  summer  just  before  fruit-bud  formation  in 
order  that  the  buds  which  remain  may  have  available  all  the  nourish- 
ment which  otherwise  would  be  more  or  less  evenly  distributed  over 
the  entire  top. 

Such  a  line  of  reasoning  is  fallacious  because  the  leaf  area  is  just 
as  important  in  the  nutrition  of  fruit-buds  as  is  the  root  system,  and 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES 


19 


to  remove  a  large  portion  of  this  manufacturing  area  just  as  the  tree 
is  beginning  to  store  food  (page  10)  robs  the  plant  to  that  extent,  and 
at  the  same  time  may  start  new  growth  which  will  also  take  additional 
food  materials. 

In  order  to  determine  the  influence  of  summer  pruning  at  the 
time  of  active  fruit-bud  development,  forty-eight  Muir  peach  trees — 
three  rows  of  sixteen  trees  each — planted  in  February,  1912,  and  rather 
severely  thinned  and  headed  in  February,  1913,  1914,  1915,  and  1916, 
were  pruned  as  follows  between  August,  1916,  and  August,  1920 : 

Row  1. — Thinned  and  headed  moderately  in  February  of  each 
year — dormant  season.     (No  summer  pruning.) 

Row  2. — Thinned  moderately  in  early  August  each  summer. 
Headed  moderately  in  February  each  winter,  thus  rendering  trees  in 
this  row  similar  in  height  to  trees  in  rows  1  and  3.  (Moderate  summer 
pruning.) 

Row  3. — Thinned  and  headed  moderately  in  early  August  each 
summer  and  when  necessary  the  older  wood  thinned  out  in  winter. 
(Heavy  summer  pruning.) 

Considering  the  average  yield  to  the  tree  of  the  sixteen  trees  in 
row  1  as  100,  the  production  for  row  2  and  row  3  was  that  indicated 
in  Table  2.3 

TABLE  2 
Average  Yield  of  Muir  Peach  Trees  With  and  Without  Summer  Pruning 


Year 

Rowl 
Winter  Thinned 
Winter  Headed 

Row  2 

Summer  Thinned 

Winter  Headed 

Row  3 
Summer  Thinned 
Summer  Headed 

1917 

100— (  51  lbs.) 
100— (  43  lbs.) 
100— (203  lbs.) 
100— (116  lbs.) 

133— (  78  lbs.) 
158— (  68  lbs.) 
100— (204  lbs.) 
115— (134  lbs.) 

98— (  50  lbs.) 

1918 

128— (  55  lbs.) 

1919 

67— (136  lbs.) 

1920 , 

90— (104  lbs.) 

Total 

100— (413  lbs.) 

117— (484  lbs.) 

83— (345  lbs.) 

During  the  season  of  1919  the  crop  from  row  2  did  not  appreciably 
exceed  that  from  the  trees  receiving  only  a  moderate  winter  pruning. 
The  increased  yields  in  row  2  during  the  other  years  were  due  perhaps 
to  admission  of  sunlight  to  the  interior  and  lower  portions  of  the 


3  The  difference  recorded  in  Tables  2  and  3  are  perhaps  not  statistically 
significant,  but  since  the  tendencies  shown  are  exactly  in  accord  with  the  results 
of  other  experiments  and  with  observations  extended  over  many  years,  it  seems 
desirable  to  include  these  data.  The  reader  should  realize,  however,  that  any 
figures  presented  in  connection  with  experiments  with  plants  merely  indicate 
general  tendencies  rather  than  exact  responses  because  of  the  great  variability 
within  the  plants  themselves  and  of  the  conditions  under  which  they  grow. 


20 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


summer  pruned  trees  with  consequently  more  economical  manufacture 
and  storage  of  carbohydrates  throughout  a  larger  portion  of  the  fruit- 
ing area.  Row  3  was  materially  weakened  by  the  rather  heavy  summer 
pruning. 

Development  of  Trees. — That  summer  pruning  of  the  Muir  peach 
as  practiced  in  these  experiments  is  devitalizing  is  shown  not  only  by 
the  trees  themselves,  but  also  by  measurements  of  the  trunks,  which 
seem  a  fair  indication  of  both  root  and  top  development. 

It  has  been  shown4  that  trunk  circumference  measurements  may 
be  confidently  depended  upon  as  a  reliable  index  of  the  total  develop- 
ment of  the  young  tree,  both  root  and  top.  It  will  be  seen  from  the 
figures  presented  below  that  summer  pruning  may  lessen  the  chance 
for  future  crops  by  limiting  tree  growth. 


TABLE  3 

Average  Trunk  Circumference  of  Trees 


Year 

Rowl 
Winter  Thinned 
Winter  Headed 

Row  2 

Summer  Thinned 

Winter  Headed 

Row  3 
Summer  Thinned 
Summer  Headed 

Nov.  1919 

50.8  cm. 
54.5  cm. 
56.7  cm. 

50.1  cm. 

51.2  cm. 
53.8  cm. 

43.9  cm. 

Nov.  1920 

46.5  cm. 

Nov.  1921 

49.3  cm. 

PEUNING  SYSTEMS 

In  recent  years  there  has  been  much  discussion  in  California  regard- 
ing the  relative  merits  of  the  so-called  "long"  and  "short"  pruning 
of  deciduous  fruit  trees.  It  is  rather  difficult  to  draw  a  definite  line 
of  demarcation  between  these  two  systems  because  with  their  modi- 
fications they  merge  into  each  other. 

Briefly,  it  may  be  said  that  the  system  of  "short"  pruning  consists 
essentially  in  a  more  or  less  severe  thinning  out,  accompanied  by  a 
heavy  heading  of  the  new  growth ;  while  the  system  of  "long"  pruning 
consists  essentially  in  a  moderate  thinning  out  and  in  keeping  the  tree 
within  bounds  by  cutting  to  laterals  which  are  left  untouched.  The 
latter  system  removes  somewhat  less  wood,  but  the  conclusion  of  many 
growers  that  it  really  amounts  to  little  or  no  pruning  is  incorrect. 

There  has  been  a  tendency  throughout  the  state  towards  less  severe 
pruning  so  that  it  is  now  becoming  increasingly  difficult  to  distinguish 


4  Tufts,  W.  P.  Influence  of  heavy  and  light  pruning  upon  the  growth  of 
deciduous  fruit  trees.  California  State  Dept.  Agr.  Mo.  Bull.  8:  529-535, 
figs.  139-140.     1919. 


Bulletin  386]      pruning  bearing  deciduous  fruit  trees  21 

between  orchards,  which  are  "short"  and  those  which  are  "long" 
pruned.  Thoughtful  and  observing  orchardists  are  beginning  to 
realize  that  the  same  principles  of  plant  growth  and  response  apply 
with  equal  force  to  all  systems  of  pruning  and  as  their  idea  of  the 
relation  of  vegetative  growth,  tonnage,  quality,  and  economy  of 
orchard  management  become  clearer  they  will  realize  that  the  different 
systems  at  present  in  use  merge  into  each  other,  and  that  the  best 
system  for  any  particular  case  will  lie  at  some  point  between  the 
extremes  of  "short"  and  "long"  pruning. 


Fig.  7. — Winters  System  .of  apricot  pruning.     Note  low  spreading  top  and 
severity  with  which  new  shoot  growth  has  been  headed. 

Mention  should  be  made  of  several  modifications  of  the  so-called 
short  and  long  systems  of  pruning  at  present  in  vogue  in  certain 
sections  of  California.  Undoubtedly  many  growers  who  are  following 
in  all  essential  details  one  of  these  methods  may  differ  as  to  the 
classification  here  made. 

Figure  7  shows  an  apricot  tree  trained  by  the  so-called  "Winters 
System"  (sometimes  aptly  referred  to  locally  as  the  "Wolf skill 
Hack").  This  flattened  expanse  of  the  fruiting  area  is  designed  to 
give  better  exposure  to  the  sun  with  the  object  of  ripening  the  fruit 
earlier.  It  does  not  bring  about  the  result  desired,  however,  because 
the  heavy  cutting  gives  rise  to  succulent  vegetative  growth  early  in 
the  season,  the  shade  from  which  more  than  offsets  the  advantage  of 


22 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


a  flat  head.  In  a  test5  conducted  in  the  Winters  district,  in  1919,  trees 
pruned  by  thinning  produced  larger  and  earlier  crops  than  comparable 
trees  pruned  by  the  standard  "Winters  System."  This  method  of 
training  is  also  objectionable  in  that  the  upper  sides  of  the  main 
branches  are  very  often  badly  sunburned  which  results  in  wood  decay, 
even  though  the  vegetative  growth  is  sufficient  to  shade  the  fruit  and 
retard  its  development.     Moreover,  restricting  the  height  of  the  tree 


Fig.  8. — Mature  Blenheim  apricot  tree  pruned  by  the  so-called  ' '  short ' ' 
system  which  consists  essentially  in  a  severe  thinning  out  and  heading  back  of 
new  wood  growth.  Note  lack  of  fruit-spurs  in  lower  parts  of  tree  due  to 
shading  out.     Too  many  main  scaffold  branches. 

so  that  all  work  is  done  from  a  six-foot  ladder  materially  reduces  the 
fruiting  area  and  the  possible  tonnage  of  fruit  of  high  quality. 

Figures  8  and  9  show  another  system  by  which  deciduous  tree 
fruits  are  pruned  in  California.  This  method  is  very  generally  applied 
and  consists  essentially  in  a  heavy  thinning,  accompanied  by  the 
removal  of  all  but  three  or  four  buds  on  the  shoots  which  are  headed — 
an  example  of  the  so-called  "short  pruning.'' 


s  Tufts,  W.  P.     Why  prune  bearing  apricot  trees  heavily?     California  State 
Dept.  of  Agriculture  Mo.  Bull.  8:  15-22,  figs.  10-17.    1919. 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES 


23 


Certain  growers  have  worked  out  for  their  own  conditions  quite 
satisfactory  systems  of  training'  and  pruning  which  are  distinct  depar- 
tures from  the  ordinary  methods. 


Fig.  9. — Fifteen-year-old  Bartlett  pear  tree  typically  " short"  pruned.  Note 
severe  thinning  and  heading  back.  Only  three  or  four  buds  have  been  left 
on  each  one-year  shoot 


Figure  10  shows  a  mature  peach  tree  pruned  by  the  "Sims 
System. ' '  The  relatively  few,  upright  main  scaffold  branches  clothed 
with  long,  slender  fruiting  twigs  are  characteristic  of  this  system. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  few  upright  scaffolds  are  able  to  hold  a  heavy  load  of  fruit  with 
the  minimum  of  bracing.  The  rather  narrow  spread  of  trees  thus 
pruned  is  perhaps  an  unwarranted  restriction  of  the  fruiting  area. 

One  of  the  most  interesting  departures  from  standard  pruning 
practice  is  the  so-called  "Caldewell  System"  of  pear  pruning  (fig.  11). 


Fig.  10. — Mature  peach  tree  pruned  by  the  "Sims'  System."  Note  heavy 
framework  branches.  Fruit  is  produced  on  long  pendant  "hangers. "  By  this 
unusual  method  much  fruit  is  produced  on  spurs.  Trees  after  reaching  a  certain 
height  (12  to  16  feet)  are  never  allowed  to  grow  taller. 


Briefly  stated,  this  system  consists  in  the  tying  down  of  the  upright 
one-year-old  shoots  at  an  angle  somewhat  below  the  horizontal.  The 
resultant  new  growth  arises  just  below  and  behind  the  highest  point 
of  the  bend.  Practically  all  growth  beyond  this  point  is  reproductive 
in  character  and  rapidly  develops  a  good  fruit-spur  system.     In  prin- 


Bulletin  386]      pruning  bearing  deciduous  fruit  trees 


25 


ciple  the  Caldwell  plan  is  very  similar  to  the  espalier  method  of  train- 
ing used  in  Europe.  In  both  cases  the  bending  of  the  branches  seems 
to  induce  fruitfulness. 

At  each  dormant  season  all  the  new  shoots  are  tied  down  in  such 
a  way  that  there  is  as  little  shading  as  possible  of  the  lower  branches. 
The  later  tying  is  done  to  any  convenient  point  on  either  trunk  or 
branch.  At  ten  years  of  age  few  pear  orchards  attain  the  size  and 
productiveness  of  Mr.  Caldwell's,  whose  trees,  with  the  exception  of 
the  first  winter,  have  not  been  touched  with  the  pruning  shears. 


\      \ 
\     \ 


Fig.  11. — Caldwell  System  of  pear  pruning.  Six-year-old  Bartlett  pear  tree 
which  has  been  trained  by  tying  down  new  shoots  each  year.  Note  new 
branches  which  arise  at  bend,  these  will  in  turn  be  tied  down  to  a  position  a 
little  below  the  horizontal. 


Briefly,  the  advantages  claimed  for  the  method  are :  large  trees  of 
good  mechanical  strength,  combined  with  a  large  fruiting  area  close 
to  the  ground,  are  secured  in  a  comparatively  short  period  of  years; 
they  come  into  bearing  from  two  to  four  years  earlier  than  trees  which 
are  trained  by  severe  cutting  back;  they  can  be  trained  to  a  more 
shapely  form  in  a  windy  section  or  where  prevailing  winds  hinder 
symmetrical  development;  and  finally,  they  produce  larger  crops  of 
equal  quality. 

The  chief  disadvantage  is  that  this  system  to  be  successful  must  be 
part  of  a  comprehensive  and  intensive  orcharding  programme.     Since 


26 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


all  wood  is  conserved,  special  care  must  be  exercised  to  see  that  ade- 
quate moisture  and  fertility  are  present  in  order  to  secure  an  abun- 
dance of  new  wood  and  at  the  same  time  carry  large  crops  through  to 
maturity  and  to  supply  the  enormous  leaf  area  which  is  being  increased 
from  year  to  year.  In  most  soils  some  renewal  pruning  will  un- 
doubtly  be  necessary  as  soon  as  the  trees  begin  bearing  heavily  in  order 


Fig.  12. — A  well  made  pruning  cut.  Note  callus  formation  which  in  the 
course  of  a  few  years  will  completely  cover  the  large  wound.  Compare  size  of 
cut  with  the  quarter-dollar. 


to  replace  the  fruiting  wood  which  has  outlived  its  usefulness  and  to 
maintain  a  proper  condition  of  vegetative  vigor.  Success  depends 
very  largely  upon  the  skill  and  judgment  of  the  individual.  The 
method  is  probably  applicable  only  to  pears  and  should  not  be 
adopted  without  a  full  understanding  of  its  requirements  and 
limitations. 


Bulletin  38G]      pruning  bearing  deciduous  fruit  trees  27 

In  adopting  any  pruning  system,  the  first  and  most  important 
question  to  be  asked  is :  "  Will  this  method  insure  the  annual  produc- 
tion of  a  good  tonnage  of  fruit  of  high  quality?"  The  growth  of 
new  wood  is  probably  the  only  index  by  which  the  grower  can  judge 
whether  or  not  future  yields  are  being  sacrificed  for  the  sake  of  one 
or  two  heavy  crops.  On  the  other  hand,  the  production  of  too  great 
an  amount  of  vegetative  growth  will  reduce  the  yields  far  below  the 
maximum  which  can  profitably  be  maintained. 


Fig.  13. — Improperly  made  pruning  cuts.     Such  stubs  will  never  heal  over 
and  are  a  constant  menace  as  affording  an  entrance  to  wood  rotting  organisms. 


PROTECTION  OF  PRUNING  WOUNDS 

If  a  tree  is  properly  pruned  from  the  start,  the  removal  of  large 
limbs  can  for  the  most  part  be  avoided. 

All  cuts  should  be  made  close  to  the  branch  from  which  the  limb 
is  taken  (fig.  12),  leaving  no  stub  (fig.  13).  This  will  greatly  facilitate 
the  healing  of  the  wounds. 

The  treatment  of  pruning  wounds  depends  largely  upon  local 
conditions.  In  any  section,  like  the  Watsonville  apple  district,  where 
the  foggy  climate  favors  the  germination  and  growth  of  the  fungi 
which  cause  wood  decay,  it  is  best  to  disinfect  the  pruning  cuts  as 


28  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

soon  as  the  wood  has  dried  a  little,  but  before  any  cracks  have  formed. 
Cyanide  of  mercury,  one  part  to  1000  parts  of  water  by  weight,  is  a 
good  disinfectant.  The  solution  should  not  be  put  into  a  metal  con- 
tainer. Containers  made  of  wood,  glass,  or  enamelware  should  be 
used.  Cyanide  of  mercury  is  a  stomach  poison  and  must  be  handled 
with  care. 

In  localities  where  the  air  is  relatively  dry,  it  will  ordinarily  be 
unnecessary  to  disinfect  pruning  wounds,  but  in  any  case  large  prun- 
ing wounds  should  be  covered  with  some  protective  substance.  This 
is  not  to  aid  the  healing,  but  to  prevent  the  entrance  of  rot-causing 
fungi.  All  wounds  an  inch  and  a  half,  or  more,  in  diameter  should 
be  covered. 

The  following  are  three  of  the  best  materials  for  covering  wounds : 

White  lead  paint  mixed  with  raw  linseed  oil. 

Asphaltum,  Grade  D,  which  must  be  heated  before  applying. 

Oronite,  which  is  similar  to  asphaltum,  but  which  can  be  applied 
cold.  When  too  thick,  a  special  non-injurious  "oronite  thinner"  can 
be  added. 

PEACTICAL  SUGGESTIONS 

1.  The  total  amount  of  new  growth  which  the  tree  makes,  taking 
into  consideration  the  crop  produced  and  the  conditions  under  which 
it  is  grown,  is  the  best  criterion  by  which  to  judge  whether  or  not  the 
pruning  has  been  of  the  proper  severity  (page  14). 

(a)  If  the  resultant  new  growth  is  longer  than  seems  desirable  for 
a  tree  of  the  kind  and  conditions  under  which  it  is  grown,  then  the 
previous  pruning  was  too  severe  (page  12). 

(&)  If  the  new  growth  has  been  inadequate  the  cutting  was  too 
light  and  a  heavier  pruning  programme  should  be  adopted,  except  in 
those  cases  where  sparse  growth  has  resulted  from  non-availability  of 
carbohydrates. 

2.  The  pruning  should  include  adequate  thinning  out  of  the  fruit- 
ing shoots,  and  this  should  be  followed,  where  necessary,  by  a  thorough 
thinning  of  the  fruit  (page  18). 

3.  The  tree  should  be  thinned  out  sufficiently  to  admit  an  adequate 
light  supply  (page  18). 

4.  All  interfering  branches,  dead  wood,  and  diseased  parts  should 
be  removed. 

5.  The  larger  limbs  should  be  spaced  far  enough  apart  throughout 
their  length  so  that  they  will  have  ample  room  to  develop  the  desired 
fruiting  branches  and  spurs. 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  29 

6.  The  trees  may  be  kept  from  becoming  too  high  by  regularly 
cutting  back  the  tallest  branches  to  strong  outward  growing  laterals. 

7.  All  branches  should  be  cut  off  close  to  the  limb  from  which  they 
arise,  leaving  no  stubs  (page  27). 

8.  It  should  be  emphasized  at  this  point  that  it  is  impossible  to 
secure  an  ideal  shape,  height,  and  distribution  of  fruiting  wood  unless 
the  trees  are  spaced  far  enough  apart  when  planted  to  enable  them 
to  develop  normally.  There  has  been  a  decided  tendency  among 
California  fruit  growers  to  plant  their  trees  too  close  together  for 
normal  development. 

TEEATMENT  FOR  THE  DIFFERENT  FRUITS 

Almonds. — The  almond  produces  its  fruit  largely  on  short  spurs, 
although  some  nuts  are  found  on  one-year  wood,  especially  in  certain 
varieties  such  as  the  Jordan  and  California.  The  fruiting  branch  of 
the  almond  remains  economically  productive  for  about  five  years. 

For  the  sake  of  economy,  the  pruning  of  bearing  almonds  is  usually 
restricted  to  the  removal  of  limbs  one-half  inch  to  an  inch  and  a  half 
in  diameter.  Little  or  no  time  is  spent  in  thinning  out  one-year  shoots, 
except  for  the  removal  of  water-sprouts  which  are  frequently  abundant. 

This  practice  is  probably  satisfactory  when  the  pruning  is  done 
annually  and  conditions  are  such  that  it  results  in  sufficient  new 
growth  to  cause  a  continual  renewal  of  the  fruit-spurs.  Approxi- 
mately one-fifth  of  the  fruiting  wood  should  be  replaced  each  season. 
Trees  under  ten  or  twelve  years  of  age  can  be  expected  to  make  from 
nine  to  eighteen  inches  of  new  growth  over  the  tree  as  a  whole,  while 
older  trees  should  make  from  six  to  ten  inches.  Many  old  almond 
orchards  do  not  make  six  inches  of  new  growth  each  year,  but  it  is 
very  probable  that  the  average  production  would  be  increased  if  the 
pruning  were  sufficiently  heavy  to  induce  this  amount.  The  cutting 
of  trees  lacking  in  vigor  should  consist  of  a  rather  heavy  pruning  of 
the  type  mentioned  above  together  with  some  cutting  back  of  the  tops 
to  large  lateral  limbs  and  some  thinning  of  the  smaller  shoots  and 
fruiting  branches. 

It  may  be  said  that  in  general  the  almond  tree  does  not  need  to 
be  thinned  out  quite  so  much  as  other  trees  because  of  the  fact  that  its 
foliage  is  rather  sparse,  and  hence  light  readily  filters  through  the 
branches.  Furthermore,  the  almond  is  seldom,  if  ever,  pruned  with 
the  idea  in  mind  of  preventing  overbearing,  since  it  does  not  produce 
a  crop  heavy  enough  to  break  any  of  the  limbs  and  the  yield  of  the  tree 
is  of  more  importance  than  the  size  of  the  nuts. 


30  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

On  account  of  the  fact  that  almonds  are  not  picked  by  hand  it  is 
not  essential  to  keep  the  tree  as  low  as  with  most  fruits.  It  is  well, 
however,  to  keep  them  low  enough  so  that  all  the  nuts  can  be  reached 
from  the  ground  with  a  pole  not  longer  than  sixteen  feet. 

On  very  rich  soils  with  a  plentiful  supply  of  moisture,  the  trees 
may  make  an  excessive  wood  growth  at  the  age  when  they  should  be 
coming  into  bearing.  Since  pruning,  except  under  conditions  where 
carbohydrates  are  limiting,  is  one  of  the  factors  which  tend  to  stimu- 
late vegetative  growth,  the  rational  procedure  in  such  a  case  seems  to 
be  to  stop  pruning  for  a  year  or  two.  This  will  tend  to  throw  the  trees 
into  bearing  and  curb  the  heavy  growth.  After  the  bearing  habit  is 
once  thoroughly  established,  pruning  may  be  resumed. 

Apples. — Most  varieties  of  apples  generally  produce  fruits  termin- 
ally on  spurs  which  are  found  on  wood  that  is  two  years  old  or  older. 
The  life  of  an  individual  apple  spur  is  frequently  as  much  as  fifteen 
or  twenty  years,  but  in  most  orchards  the  period  over  which  a  spur 
bears  sufficiently  often  to  be  an  important  factor  in  production  is  not 
over  eight  or  ten  years.  Frequently  these  terminal  producing  spurs 
fruit  in  alternate  years.  Unfavorable  weather  conditions  may  prevent 
most  of  the  spurs  from  bearing  in  a  particular  year,  and  as  a  conse- 
quence, a  very  heavy  crop  will  be  produced  the  next.  These  trees  will 
very  likely  then  be  thrown  into  the  habit  of  alternate  bearing.  There 
are,  however,  certain  notorious  alternate  bearing  varieties  such  as  the 
Oldenburg,  Baldwin  and  Wealthy,  which  may  firmly  establish  the 
alternating  habit  regardless  of  weather  conditions.  In  California  it 
very  often  happens  that  a  spur  elongates  and  sets  a  terminal  fruit-bud 
during  the  same  summer  that  it  is  maturing  fruit,  in  which  case  the 
tendency  towards  alternate  bearing  is  broken.  Possibly  one  of  the 
best  methods  of  circumventing  the  alternate  bearing  habit  is  to  keep 
the  trees  in  such  a  state  of  vegetative  vigor  that  only  half  or  less  than 
half  of  their  spurs  bloom  in  any  one  year. 

While  the  major  part  of  the  apple  crop  is  commonly  borne  on  spurs, 
a  smaller  portion  is  produced  on  one-year  wood.  This  is  particularly 
true  of  young  trees  of  certain  varieties,  such  as  the  Gravenstein,  Ben 
Davis,  Jonathan  and  Winesap.  Varieties  differ  as  to  the  part  of  the 
shoot  on  which  the  fruit  is  developed.  Normally,  the  fruit-buds  are 
borne  either  terminally  or  laterally  near  the  apex.  Varieties  that 
produce  an  abundance  of  fruit-buds  on  the  one-year  wood  usually 
come  into  bearing  at  an  earlier  age  and  are  more  likely  to  bear  annually 
than  those  that  fruit  entirely  on  spurs. 

A  thinning  out  of  the  branches  to  admit  sufficient  light  to  penetrate 
to  all  parts  of  the  tree  is  a  prime  consideration  in  causing  new  spurs 
to  develop  and  in  aiding  those  that  already  exist  to  bear  regularly. 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  31 

Many  varieties  of  apples  tend  to  over-bear,  especially  in  the 
alternate  years,  and  as  a  result  the  fruit  requires  a  great  deal  of  hand- 
thinning.  The  type  of  pruning  that  will  encourage  annual  bearing 
and  reduce  the  amount  of  hand-thinning  that  is  necessary  is  that  which 
tends  to  reduce  the  crop  somewhat  and  to  invigorate  the  trees  in  the 
alternate  years  when  they  have  a  heavy  set  of  fruit-buds.  This  may 
be  done  not  only  by  thinning  the  shoots  and  branches,  but  also  by 
thinning  out  the  spurs,  and  renewing  the  long,  much  branched  ones  by 
removing  the  older  parts  of  the  spurs  and  saving  the  newer,  i.e.,  by 
"spur  pruning.'7  The  pruning  particularly  in  reference  to  the  fruit- 
buds  and  spurs,  should  be  much  lighter  the  following  year,  when  the 
tree  has  comparatively  few  fruit-buds. 

In  general,  the  apple  does  not  require  heavy  pruning.  On  account 
of  its  habit  of  bearing  largely  on  long-lived  spurs,  approximately  only 
10  per  cent  of  which  must  be  replaced  each  year,  it  requires  somewhat 
less  new  wood  growth  than  some  other  fruits.  The  young  bearing 
apple  tree  should  ordinarily  make  from  ten  to  twenty  inches  of  new 
wood  growth  each  year,  while  with  the  older  trees  six  to  ten  inches  is 
sufficient.  This  amount  of  new  wood  growth  can  ordinarily  be  secured 
by  cutting  back  to  laterals,  leaving  a  few  of  the  one-year-old  "shoots 
intact.  However,  if  the  wood  growth  shows  a  tendency  to  drop  below 
the  above  mentioned  minimum  amounts,  heading  back  the  laterals 
which  are  left  after  thinning  may  be  necessary  to  secure  the  proper 
vigor. 

A  thorough  thinning  out  of  the  tree  is  of  special  importance  in  the 
case  of  varieties  having  red  fruit,  as  highly  colored  apples  are  the 
result  of  abundant  light  supply  throughout  the  tree.  While  it  has 
been  stated  that  in  general  summer  pruning  does  not  seem  desirable 
for  bearing  trees,  it  is  possible  that  a  light  summer  thinning  may  be 
beneficial  in  securing  a  better  color  of  the  fruit  on  trees  of  red  varieties, 
having  foliage  which  is  rather  thick  and  dense. 

The  apple  powdery  mildew  (Sphaerotkeca  leucotricha  (Ell.  &  Ev.) 
Salm.)  which  has  done  considerable  damage  to  the  apple  orchards  in 
California,  particularly  in  the  humid  coastal  regions,  can  be  largely 
controlled  by  proper  pruning  in  conjunction  with  spraying.  The 
pruning  treatment  in  this  respect  consists  in  removing  the  diseased 
shoots  and  spurs  at  the  regular  dormant  pruning,  and  thus  eliminating 
the  sources  of  hold-over  infection.  Mildewed  shoots  are  easily  recog- 
nized by  their  gray  or  silvery  appearance. 

The  undesirability  of  removing  large  limbs  has  already  been 
pointed  out  (page  27),  but  it  must  be  emphasized  again  that  it  is 
especially  dangerous  to  cut  off  main  branches  in  damp  coastal  dis- 


32 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


tricts,  such  as  the  Pajaro  Valley.  When  limbs  more  than  an  inch  and 
a  half  in  diameter  are  removed  it  is  very  probable  that  a  serious  wood- 
and-bark  disease,  known  locally  as  "sappy  bark,"  will  develop.  The 
serious  nature  of  the  malady  will  be  apparent  from  the  fact  that  it 
often  travels  down  the  limb  from  a  large  wound  and  eventually  reaches 
the  trunk  and  kills  the  tree.  Disinfecting  and  painting  the  wounds 
has  not  as  yet  proved  effective  in  preventing  the  disease. 

Apricots. — The  apricot  produces  the  bulk  of  its  fruit  laterally  on 
spurs  which  generally  do  not  live  more  than  three  years.  A  relatively 
small  portion  of  the  crop  is  produced  laterally  on  one-year  shoots. 

Since  the  fruit-spur  system  of  the  apricot  is  short-lived,  the  pruning 
treatment  must  be  such  as  to  cause  its  continual  renewal.  Young 
bearing  apricot  trees  should  make  from  fifteen  to  thirty  inches  of  new 
growth  each  year.  On  older  trees  the  desirable  length  of  new  growth 
ranges  from  ten  to  twenty-four  inches.  The  peach  and  Japanese 
plums  are  probably  the  only  fruits  that  ordinarily  require  a  heavier 
pruning  than  the  apricot  in  order  to  produce  sufficient  new  growth 
for  continued  profitable  production. 


TABLE  4 
Yield  of  Six-Year-Old  Eoyal  Apricots,  1922 


Pruning  treatment 

Average  yield  per  tree 

Average  size  of  fruit 

Thinned  and  headed  severely 

23.9  lbs. 
200.6  lbs. 

8.3  fruits  per  lb. 
13.4  fruits  per  IK 

Thinned  out  and  cut  to  laterals 

Particular  pains  should  be  taken  not  to  allow  the  branches  to 
become  too  long,  willowy  and  unbranched.  This  condition  can  best 
be  avoided  by  cutting  back  to  laterals.  As  the  tree  becomes  older  and 
only  a  short  growth  follows  a  thinning  system  of  pruning,  it  is  quite 
possible  that  a  more  severe  type  of  cutting  will  have  to  be  used  to 
maintain  the  vigor  of  the  tree. 

The  apricot  is  one  of  the  fruits  which  has  in  the  past  in  California 
been  very  commonly  subjected  to  heavy  pruning  regardless  of  the  age 
and  vigor  of  the  trees.  The  yield  record  of  a  six-year-old  Royal  apricot 
orchard  given  in  Table  4  is  interesting  in  this  connection.  The  orchard 
was  planted  at  the  University  Farm  at  Davis  in  February,  1916.  It 
is  growing  on  a  sandy  loam  of  the  Yolo  series  and  all  trees  have 
received  the  same  good,  uniform,  commercial  culture  except  as  regards 
pruning  treatment.  In  each  case  the  figures  are  the  average  of  sixteen 
trees  in  a  single  block  receiving  the  same  pruning  treatment. 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES 


33 


These  figures  bring  out  very  strikingly  the  influence  of  heavy  and 
light  pruning  on  young  bearing  apricot  trees. 

As  the  tree  becomes  older,  the  continuance  of  a  comparatively  light 
system  of  pruning,  especially  in  the  absence  of  adequate  soil  moisture, 
will  usually  result  in  a  slowing  down  of  wood  growth  and  a  consequent 
falling  off  in  yield. 

This  fact  is  rather  clearly  demonstrated  in  Table  5,  which  shows 
the  yield  records  over  a  series  of  years  for  a  block  of  fifteen  Tilton 
apricot  trees,  five  trees  to  a  treatment.6  The  trees  in  question  were 
all  planted  in  the  University  orchards  at  Davis  in  March,  1908,  and 
were  thinned  out  and  headed  severely  from  1909-1915  inclusive,  the 
pruning  experiment  starting  the  next  year.  With  the  exception  of  the 
pruning,  these  trees  have  received  identical  cultural  treatment. 

TABLE  5 
Average  Yield  of  Tilton  Apricot  in  Pounds  per  Tree 


Pruning  treatment 

Thinned   and   headed   se 

verely 

Thinned  and  headed  light 

ly 

Thinned  out  only 


1916 

1917 

1918 

1919 

1920 

1922 

1923 

23 

59 

50 

88 

30 

53 

58 

20 

119 

107 

169 

252 

241 

74 

77 

171 

146 

137 

172 

214 

107 

Average 


52 

140 
146 


It  will  be  observed  that  the  lighter  pruning  resulted  during  the 
very  first  year  in  a  marked  increase  in  yield  over  that  obtained  from 
the  trees  headed  back.  The  greater  yield  of  the  thinned  trees  was  due 
to  the  production  of  fruit  on  the  one-year  wood,  which  was  removed 
from  the  trees  which  received  a  heavy  or  light  heading.  The  com- 
paratively low  yield  of  the  trees  during  this  year  is  very  largely 
accounted  for  by  the  fact  that  these  trees  had  been  accorded  a  very 
heavy  cutting  from  the  beginning  with  consequent  shading  out  of  all 
fruit  spurs  by  the  denseness  of  the  vegetative  growth  thus  secured. 

For  the  first  three  years  the  yields  were  approximately  inversely 
proportional  to  the  severity  of  the  pruning.  By  1919  the  results  of 
the  lighter  pruning  and  heavier  fruiting  were  evidenced  by  the  larger 
yield  of  trees  which  were  lightly  headed,  and  for  the  following  two 
seasons  the  trees  receiving  this  treatment  retained  this  lead.  This 
was  naturally  to  be  expected  in  view  of  the  decreased  wood  growth  on 


6  It  is  realized  that  the  number  of  trees  included  in  each  plot  is  too  small  to 
give  the  data  statistical  reliability;  nevertheless  the  figures  are  presented  since 
they  bear  out  the  author's  observations  in  hundreds  of  California  orchards.  It 
is  not  intended  that  the  yields  and  sizes  in  any  of  the  tables  should  be  taken 
as  an  exact  measure  of  the  results  obtained,  but  merely  as  showing  tendencies. 


34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

the  very  lightly  pruned  trees  which  had  no  way  of  renewing  their 
fruit-spur  systems.  There  was  no  crop  in  1921  on  account  of  killing 
frosts. 

The  heavily  headed  trees  matured  their  crop  from  a  week  to  ten 
days  later  than  those  which  received  only  a  light  heading  or  simply  a 
thinning  treatment.  This  fact  is  of  significant  importance  in  those 
sections  where  the  fruit  is  primarily  intended  for  eastern  shipment. 

Although  the  fruit  was  slightly  larger  on  the  severely  pruned  trees, 
the  size  has  been  entirely  satisfactory  in  the  other  treatments  as  may 
be  seen  from  the  following  average  for  a  six-year  period.  However, 
the  fact  should  be  recognized  that  in  some  sections  of  the  state  and 
especially  with  older  trees  very  light  pruning  may  result  in  fruit  of 
inferior  size. 

TABLE  6 
Average  Size  of  Fruit  per  Pound — Tilton  Apricot,  1916-1922 


Pruning  treatment 

Average  size  of  fruit 

Thinned  out  and  headed  severely 

8.9  fruits  per  lb. 

Thinned  out  and  headed  lightly 

10.7  fruits  per  lb. 

Thinned  out  only 

10.8  fruits  per  lb. 

These  data  lend  further  weight  to  the  argument  that  it  is  necessary 
to  maintain  the  vegetative  activity  of  the  bearing  fruit  tree  if  con- 
tinued profitable  production  is  to  be  secured.  Under  conditions  exist- 
ing in  this  part  of  the  University  orchards,  where  no  irrigation  facili- 
ties were  available,  it  is  quite  evident  that  it  was  impossible  to  main- 
tain a  proper  balance  between  fruit  production  and  wood  growth  by  a 
reliance  on  a  thinning  out  system  of  pruning  unaccompanied  by  head- 
ing. In  other  words,  lack  of  irrigation  brought  about  a  depletion  of 
soil  moisture  which  either  killed  a  certain  number  of  roots  or  rendered 
them  for  the  time  being  incapable  of  functioning  thus  reducing  the 
feeding  area  and  destroying  the  balance  between  carbohydrates  and 
available  mineral  nutrients,  which  is  necessary  for  the  best  production 
of  fruit. 

In  sections  which  are  subject  to  the  ravages  of  the  brown  rot 
(Sclerotinia  cinerea  (Bon)  Schrot.),  efforts  should  be  made  to  remove 
all  infected  spurs  and  shoots,  as  these  continue  to  produce  spores  of 
the  fungus  throughout  the  winter  and  spring  and  make  control  by 
spraying  more  difficult. 

The  pruning  of  trees  infected  with  bacterial  gummosis  (Bacterium 
cerasi  Griffin)  warrants  special  mention.  This  disease  is  characterized 
by  gumming  cankers  on  the  trunks  and  larger  limbs  during  the  winter 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  35 

and  spring  months,  and  if  not  carefully  and  promptly  treated  may 
girdle  the  affected  parts  and  cause  their  death.  The  disease  is  caused 
by  bacteria  and  may  be  readily  spread  from  one  tree  to  another  by 
pruning  tools.  In  case  this  malady  is  known  to  exist  in  an  orchard, 
it  is  a  wise  precaution  to  disinfect  the  shears  and  saw  used  in  pruning 
after  finishing  each  tree.  A  solution  of  bichloride  of  mercury,  one 
part  by  weight  to  500  parts  of  water,  is  a  satisfactory  disinfectant. 
If  the  solution  is  to  be  used  for  treatment  of  the  cankers  as  well  as 
for  a  disinfectant  for  the  tools,  it  should  contain  also  cyanide  of 
mercury  one  part  by  weight  to  500  parts  of  water. 

Sweet  Cherries. — Sweet  cherries  are  borne  laterally  on  long-lived 
spurs  which  are  economically  productive  for  ten  or  twelve  years.  On 
account  of  this  persistence  of  the  fruit-spur  system,  the  sweet  cherry 
needs  less  renewal  wood  than  practically  any  other  deciduous  fruit. 
If  the  trees  have  been  properly  trained  and  brought  into  bearing,  but 
little  pruning  is  necessary  to  maintain  them  in  a  productive  condition. 
That  pruning  which  is  necessary,  however,  should  be  done  annually 
and  should  be  of  sufficient  severity  to  renew  approximately  ten  per 
cent  of  the  fruit  bearing  area  each  year. 

It  is  characteristic  of  the  sweet  cherry  tree  to  produce  most  of  its 
new  growth  from  terminal  buds.  There  is,  therefore,  a  decided 
tendency  to  develop  long  pole-like  branches  if  no  heading  is  done.  It 
is  usually  considered  necessary  to  cut  back  cherry  trees  moderately  the 
first  four  or  five  years,  or  until  such  time  as  the  framework  is  com- 
pleted. After  the  first  few  years,  the  further  heading  will  cause 
delay  in  fruiting,  and  the  desired  form  can  generally  be  attained 
without  resorting  to  this  practice.  The  cherry  is  slow  in  coming  into 
bearing  and  just  as  long  as  new  wood  growth  is  encouraged  by  rather 
heavy  cutting,  the  tree  will  make  only  shoot  growth  and  fail  to  develop 
fruit-spurs. 

As  the  sweet  cherry  tree  is  naturally  upright  in  growth,  care  should 
be  taken  to  give  it  as  much  spread  as  possible  by  retaining  the  outward 
growing  shoots  and  removing  the  upright  ones.  This  is  of  special 
importance  with  such  upright  growing  varieties  as  the  Lambert  and 
Black  Tartarian.  The  Napoleon  (Royal  Ann)  naturally  assumes  a 
spreading  habit  with  age.  Certain  cherry  growers  have  had  consider- 
able success  in  keeping  their  trees  low  by  very  little  if  any  pruning 
during  their  earlier  years,  thus  forcing  them  into  rather  precocious 
fruiting  and  allowing  the  weight  of  the  crops  to  bring  about  the  desired 
spread.  Careful  judgment,  however,  must  be  used  in  adopting  such 
a  plan. 


36  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  cherry  tree  is  very  particular  as  to  the  conditions  under  which 
it  will  thrive.  It  is  particularly  susceptible  to  drought  and  excessive 
soil  moisture.  The  reinvigoration  of  weak  trees  is  a  more  complicated 
problem  than  the  mere  adoption  of  a  rational  pruning  method.  In 
order  to  keep  a  bearing  cherry  orchard  in  a  good  state  of  vigor,  par- 
ticular emphasis  must  be  laid  on  proper  soil  conditions.  When  it  is 
found  necessary  to  cut  back  cherry  trees  into  older  wood,  either  for 
the  purpose  of  lowering  the  trees  or  of  stimulating  the  wood  growth, 
care  should  be  taken  to  cut  to  a  lateral,  wherever  possible.  Trees 
showing  much  die-back  of  the  leading  branches  can  sometimes  be 
rejuvenated  by  rather  severe  pruning.  However,  it  should  be  men- 
tioned again  that  soil  conditions  must  at  the.  same  time  be  improved. 

The  sweet  cherry,  like  the  apricot,  is  susceptible  to  bacterial 
gummosis.  Suggestions  regarding  the  handling  of  apricot  trees  suffer- 
ing from  this  disease  apply  with  equal  force  to  cherries. 

Peaches  and  Nectarines. — The  fruiting  habit  of  the  nectarine  is 
practically  identical  with  that  of  the  peach. 

There  is  probably  no  other  fruit  which  responds  to  proper  pruning 
and  which  declines  with  neglect  so  readily  as  the  peach.  This  behavior 
is  largely  explained  by  the  fact  that  the  peach  bears  its  crop  almost 
entirely  on  one-year-old  wood.  Only  occasionally  is  fruit  found  on 
spurs,  and  these  are  very  short-lived.  For  this  reason  it  is  necessary 
to  prune  peach  trees  more  heavily  than  most  other  fruits  in  order  to 
produce  sufficient  fruit-bearing  wood  each  year.  Twenty  to  forty 
inches  of  growth  over  the  tree  as  a  whole  is  not  excessive  for  young 
bearing  trees.  Older  trees  may  be  expected  to  produce  each  season  an 
abundance  of  shoots  of  from  twelve  to  thirty  inches  in  length. 

It  is  characteristic  of  the  peach  that  its  bearing  area  is  carried 
higher  and  higher  each  year,  leaving  long  stretches  of  non-fruiting 
branches  that  are  subject  to  sunburn  and  decay  and  that  serve  only 
as  a  connection  between  the  fruiting  periphery  of  the  tree  and  its 
sources  of  water  and  mineral  nutrients — the  roots.  The  denseness  of 
the  foliage  of  the  peach  makes  it  difficult  to  maintain  a  satisfactory 
distribution  of  the  fruiting  wood  in  the  interior  of  the  tree.  Care 
must  be  taken  to  see  that  the  trees  are  thinned  out  in  order  that  ade- 
quate light  may  reach  all  parts  and  thus  insure  the  production  of 
fruiting  branches  on  the  lower  limbs.  If  careful  attention  is  not  given 
to  this  detail  then  the  characteristic  " leggy"  peach  tree  with  sun- 
burned branches  and  practically  all  new  growth  confined  to  the 
periphery  is  the  result. 

Hanging  shoots  and  branches,  sometimes  spoken  of  as  ' '  hangers, ' ' 
are  particularly  desirable  for  fruit  bearing  on  peach  trees  and  should 


Bulletin  386]      pruning  bearing  deciduous  fruit  trees  37 

be  encouraged.  Care  should  be  exercised,  however,  to  see  that  these 
do  not  become  too  long  by  the  addition  of  a  certain  amount  of  growth 
each  year.  Such  shoots  can  frequently  be  shortened  and  renewed  by 
cutting  back  to  a  new  lateral.  Fruit  on  these  hangers  is  borne  on 
relatively  short  annual  growths  and  sometimes  on  spurs. 

In  California  it  is  seldom  that  a  peach  tree  fails  to  set  enough 
fruit-buds  for  a  heavy  crop.  In  fact,  one  of  the  most  perplexing 
problems  in  the  pruning  of  bearing  peach  trees  is  to  determine  what 
amount  of  fruiting  wood  should  be  left  to  blossom  and  mature  fruit. 
After  the  trees  have  been  thinned  of  the  superfluous  larger  branches 
and  the  desired  form  has  been  secured,  the  question  arises  as  to  how 
best  to  reduce  the  fruit-buds  to  such  a  number  that  the  crop  which  is 
likely  to  set  will  be  well  distributed  and  at  the  same  time  will  not 
impose  too  heavy  a  task  at  the  thinning  season.  Generally  speaking, 
it  is  more  economical  to  reduce  the  crop  as  much  as  possible  with  the 
pruning  shears  during  the  dormant  season  than  entirely  by  hand 
thinning  after  the  fruit  is  set.  However,  to  attempt  to  thin  with  the 
pruning  shears  so  that  no  hand-thinning  will  be  necessary  to  secure 
the  desired  size  and  quality  is  likely  to  reduce  the  total  tonnage  to  such 
a  degree  that  the  practice  will  not  be  economical. 

This  reduction  of  the  fruiting  wood  may  be  accomplished  either  by 
a  thinning  out  and  heading  back  or  a  combination  of  these  two 
methods.  Care  must  be  taken  not  to  head  the  new  shoots  on  varieties 
which  bear  only  at  the  tip  or  on  the  outer  half  of  the  shoot,  especially, 
when  the  set  of  fruit-buds  is  light.  This  method  of  fruiting  is  char- 
acteristic of  such  varieties  as  the  Tuscan  and  Phillips  Cling  peaches. 
On  the  other  hand,  the  Elberta,  Muir,  Alexander,  Early  Crawford, 
and  Lemon  Cling  are  typical  of  the  varieties  that  bear  rather  uni- 
formly throughout  the  entire  length  of  the  shoot.  With  the  latter 
varieties,  heading  of  the  fruiting  twigs  may  be  entirely  feasible  and 
in  fact  desirable. 

In  most  instances  the  proper  amount  of  fruiting  wood  should  be 
obtained  by : 

(a)  Thinning  out  the  unbranched  one-year-old  fruiting  shoots. 

(b)  Cutting  back  lightly  or  moderately  to  laterals  the  fruiting 

shoots  that  are  branched. 

(c)  Thinning  out  the  remaining  laterals  on  these  branched  shoots. 

(d)  Heading  back  the  fruiting  shoots  which  are  thus  left,  where 

experience  has  shown  this  to  be  a  desirable  practice,  either 
from  the  standpoint  of: 

1.  Thinning  the  crop  ;  or 

2.  Securing  new  wood  growth  for  the  crop  of  the  following  year. 


38 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Where  possible,  it  is  well  to  cut  to  the  brownish  colored,  stocky 
laterals  rather  than  to  shoots  that  are  slender  and  reddish  in  color,  as 
the  former  are  better  adapted  to  continue  the  framework  of  the  tree 
and  generally  produce  fruit  of  somewhat  higher  quality. 

In  cutting  back  to  a  lateral  that  is  likely  to  bear  fruit  the  following 
season,  it  is  advisable  to  leave  a  short  stub  just  above  the  lateral — a 
quarter  or  one-half  inch  long — to  prevent  the  lateral  from  being 
broken  off  by  the  weight  of  the  fruit. 


Fig.  14. — Seven-year-old  Elberta  peach  tree  before  pruning.  Note  vigorous 
new  wood  growth  which,  however,  is  not  excessive.  Compare  with  fig.  15  after 
pruning  by  thinning.     This  tree  has  been  well  pruned  during  preceding  seasons. 

Figures  14  and  15  show  a  young  bearing  peach  tree  before  and 
after  pruning.  This  tree  has  responded  well  to  a  thinning  treatment — 
so-called  "long  pruning." 

Pears. — The  fruit-bearing  habit  of  the  pear  is  almost  identical  with 
that  of  the  apple,  and  hence  suggestions  regarding  the  pruning  of  the 
apple  apply  with  equal  force  to  the  pear.  The  pear  of  course  has 
varietal  characteristics  just  as  the  apple  has.  Some  varieties  tend  to 
come  into  bearing  earlier  than  others.  Likewise,  some  varieties  such 
as  the  Bartlett,  Winter  Nelis,  and  Angouleme,  tend  to  produce  a  con- 
siderable portion  of  their  crop,  especially  during  the  early  bearing 


BULLETIN  38G]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES 


39 


years,  at  or  near  the  end  of  one-year  wood.  The  tendency  towards 
alternate  bearing  is  not  so  pronounced  in  the  pear  as  in  the  apple,  the 
fruit  spurs  are  generally  a  little  shorter,  and  the  tree  is  more  upright 
in  habit  of  growth. 

Figure  16  shows  an  ideal  shaped  Glout  Morceau  pear  tree.  Figure 
17  illustrates  the  pruning  of  a  nine-year-old  Bartlett.  Under  favorable 
soil  and  moisture  conditions,  neglected  pear  trees  sometimes  make  an 


Fig.  15. — A  well  pruned  seven-year-old  Elberta  peach  tree  pruned '  by 
"thinning  out."  Compare  with  fig.  14  before  pruning.  Note  large  amount  of 
growth  removed.  This  tree  has  been  pruned  for  four  consecutive  years  by 
thinning — no  cutting  to  stubs. 


exceptional  development  (fig.  18).  Little  or  no  pruning  is  not  to  be 
generally  recommended,  but  may  occasionally  be  used  to  advantage  on 
very  rich  and  moist  soils,  increasing  yields  and  rendering  the  trees  less 
subject  to  the  ravages  of  pear  blight  (Bacillus  amylovorous) . 

Plums  and  Prunes. — There  are  two  general  classes  of  plums  com- 
mercially cultivated  in  California — the  Japanese  and  the  European. 
The  former  includes  only  shipping  varieties,  while  the  latter  includes 
both  shipping  plums  and  prunes.  Since  the  fruiting  habit  and  the 
pruning  of  these  two  species  are  somewhat  different  it  will  be  well  to 
divide  the  discussion  into  two  parts. 


40 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Japanese  Plums. — Japanese  plums  are,  in  a  large  part,  borne 
laterally  upon  short,  thick  spurs.  The  spurs  are  found  mostly  on 
wood  of  from  two  to  six  or  eight  years  of  age.  The  life  of  a  spur  varies 
from  five  to  eight  years.    A  minor  portion  of  the  crop  is  borne  laterally 


Fig.  16. — A  well  pruned  ten-year-old  Glout  Morgeau  pear  tree.  Note  size 
of  the  few  scaffold  branches.  An  ideal  framework  capable  of  supporting 
immense  crops  without  breakage.     Compare  fig.  9. 

on  one-year  wood,  the  fruit  being  produced  in  general  at  the  basal  part 
of  the  shoot. 

The  fruit-bearing  habit  of  the  Japanese  plum  is  quite  similar  to 
that  of  the  apricot,  the  principal  difference  being  that  the  spurs  on 


Bulletin  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES 


41 


the  former  are  somewhat  longer  lived.  As  a  natural  consequence  the 
pruning  of  these  two  fruits  is  much  alike.  The  fact  that  the  spurs 
of  the  Japanese  plum  are  longer  lived  than  those  of  the  apricot  would 
lead  one  to  the  conclusion  that  these  plums  should  be  pruned  somewhat 
less  severely  than  the  apricot,  there  being  less  necessity  of  replacing 
the  fruiting  wood  with  new  shoots.  The  Japanese  plum,  however,  is 
most  prolific  and  as  only  large  fruits  are  commercially  valuable,  the 
trees  as  a  consequence  must  be  pruned  rather  heavily,  in  order  to 


Fig.  17. — A  nine-year-old  Bartlett  pear  tree  before  and  after  pruning.  This 
tree  has  been  consistently  pruned  rather  lightly,  however.  Compare  fig.  18  of 
an  adjoining  tree  which  has  not  been  pruned  for  five  years.  The  photographs 
were  taken  at  same  distance  from  each  tree. 


reduce  the  fruit  crop  and  at  the  same  time  induce  sufficient  new  wood 
growth.  As  a  final  result,  therefore,  the  severity  of  the  pruning  of 
these  two  fruits  should  be  very  similar.  The  plum  should  be  pruned 
in  such  a  way  that  some  ten  to  twenty-four  inches  of  new  wood  growth 
annually  is  secured  on  young  bearing  trees  and  ten  to  twelve  inches 
on  older  ones. 

There  is   considerable   difference  in   the  habit  of   growth   of  the 
different  varieties.     Some  varieties  such  as  the  Burbank,  are  rather 


42 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


low-spreading  growers  and  attention  must  be  paid  even  after  the  trees 
come  into  bearing  to  divert  the  growth  into  the  more  upright  branches. 
On  the  other  hand,  the  Wickson,  Kelsey,  and  Santa  Rosa  are  examples 
of  varieties  that  make  a  very  narrow,  upright  growth  and  require 
careful  pruning  to  secure  the  proper  spread. 

Figures  19  and  20  show  a  young  bearing  Climax  plum  tree  before 
and  after  pruning. 


Fig.  18. — A  nine-year-old  Bartlett  pear  tree  before  and  after  pruning. 
Deliberately  left  unpruned  for  the  five  years  preceding.  Note  splendid  develop- 
ment of  fruiting  wood  and  framework  branches.  Compare  fig.  17  of  an  adjoin- 
ing tree  which  has  been  pruned  lightly.  In  addition  to  increasing  enormously 
in  size  this  tree  has  produced  from  six  to  eight  times  as  much  fruit  as  the 
lightly  pruned  tree.  This  illustration  is  introduced  not  in  the  way  of  recom- 
mendation but  merely  to  emphasize  the  greater  development  secured  by  little  or 
no  pruning  so  long  as  the  tree  makes  sufficient  new  wood  growth. 

European  Plums. — The  fruit-spurs  of  the  European  plums  are 
quite  different  from  those  of  the  Japanese.  They  are  longer,  more 
slender,  and  frequently  branched.  Old  spurs,  or,  as  they  are  some- 
times called  ' '  fruiting  brush, ' '  may  reach  a  length  of  two  or  three  feet, 
while  the  spurs  of  Japanese  plums  are  rarely  longer  than  two  or 
three  inches. 

The  pruning  of  European  shipping  plums  is  very  similar  to  that 
of  Japanese  plums,  but  it  is  for  two  reasons  a  less  severe  type  of 


Bulletin  386]       pruning  BEARING  DECIDUOUS  FRUIT  TREES 


43 


10. 


/ 


/ 


/ 


\ 

Fig.  19. — A  young  bearing  Climax  (Japanese)  plum  tree  before  pruning. 
Note  vigorous  new  wood  growth  produced  by  thinning  method  of  pruning.  This 
tree  has  produced  several  good  crops.     Compare  with  fig.  20. 


44 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  20. — Young  bearing  Climax  (Japanese)  plum  tree  after  pruning.  Com- 
pare fig.  19  before  pruning.  This  tree  might  perhaps  have  been  somewhat  better 
handled  by  removing  two  or  three  of  the  heavier  branches  in  addition  to  the 
thinning  of  the  smaller  shoots.  A  mistake  was  made  in  the  earlier  years  in 
not  reducing  the  number  of  scaffold  limbs. 


BULLETIN  386]       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  45 

pruning.  European  plums  do  not  tend  to  over-produce  as  do  the 
Japanese,  hence,  a  light  pruning  is  sometimes  necessary  to  favor  fruit- 
bud  formation  in  the  former,  rather  than  a  severe  pruning  to  reduce 
the  quantity  of  fruit-buds  as  with  the  latter  species.  Furthermore,  a 
relatively  larger  proportion  of  the  fruit  of  the  European  plum  is 
borne  on  spurs.  Keeping  these  facts  in  mind,  the  grower  may  handle 
the  European  shipping  plums  by  much  the  same  methods  as  are 
described  for  the  Japanese  plum  and  apricot. 

The  fruiting  habit  of  prunes  is  identical  with  that  of  European 
shipping  plums.  The  only  difference  between  the  two  kinds  is  that 
in  the  case  of  the  prunes  the  mature  fruit  contains  sufficient  sugar  to 
dry  without  fermenting  at  the  pit,  while  the  latter  does  not.  Since, 
with  the  exception  of  the  Sugar  variety,  it  is  not  customary  to  thin 
the  fruit  nor  to  pick  it  from  the  tree,  no  great  attempt  has  been  made 
on  the  part  of  the  prune  growers  to  keep  their  trees  within  bounds. 
However,  the  relation  of  the  operations  of  pruning  and  spraying  to 
the  height  of  the  tree  should  not  be  overlooked. 

The  pruning  commonly  given  prune  trees  in  this  state  consists  in 
a  rather  severe  thinning  and  heading  back  of  both  the  fruiting  brush 
and  the  larger  limbs.  This  treatment  is  often  given  only  at  irregular 
and  infrequent  intervals.  Vigorous  new  shoots  arise  near  the  cuts, 
necessitating  a  severe  pruning  the  following  season.  It  often  follows 
that  two  or  three  years  may  elapse  before  the  trees  that  have  been  thus 
heavily  pruned  again  settle  down  to  good  production.  It  seems  that 
one  of  the  most  important  facts  to  be  emphasized  in  regard  to  the 
handling  of  prune  trees  is  that  the  pruning  should  be  done  regularly 
and  in  most  cases  should  be  merely  a  light  thinning  out  of  the  shoots, 
old  spurs,  and  smaller  branches  (fig.  21).  The  hanging  branches  are 
often  cut  back  to  upward  and  outward  pointing  limbs  in  order  to  keep 
the  tree  well  shaped.  From  an  economical  point  of  view  it  is  fortunate 
that  few  cuts  less  than  a  quarter  of  an  inch  in  diameter  are  necessary 
in  order  to  keep  sufficient  new  wood  growth  coming.  An  average 
yearly  extension  of  the  leading  branches  of  from  nine  to  eighteen 
inches  is  adequate  for  young  bearing  prune  trees.  Older  trees  should 
be  expected  to  make  at  least  six  inches  of  growth  each  summer. 

It  is  a  matter  of  common  observation  in  the  older  prune  orchards 
that  have  been  given  little  pruning  that  the  bearing  area  is  located  as 
a  thin  shell  on  the  periphery  of  the  tree.  A  branch  eight  feet  long,  for 
example,  often  has  all  its  fruit-spurs  on  two  or  three  feet  at  the 
terminal  end  of  the  branch  while  the  rest  of  the  limb  is  bare  and 
unproductive.  This  concentration  of  the  bearing  area  at  the  ends  of 
the  branches  is  generally  due  to  an  insufficient  amount  of  thinning, 


46 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


resulting  in  a  shading  out  of  the  interior  and  lower  fruiting  wood. 
Where  the  fruit-spurs  have  not  been  killed  they  are  often  long,  slender, 
and  unproductive  in  contrast  with  the  shorter,  stockier,  fruit-produc- 
ing spurs  to  be  found  on  the  outside  of  the  tree.  Such  shaded,  willowy 
spurs  produce  small  fruit  and  are  short-lived.  It  is  obvious  that  the 
corrective  treatment  for  such  a  condition  lies  in  an  adequate  thinning 
out  of  the  smaller  branches,  where  the  tree  has  been  properly  trained, 


&aam 


Fig.  21. — Thirty-year-old  French  prune  tree  pruned  by  the  removal  of  a  few 
of  the  larger  branches  and  a  thorough  thinning  of  the  i( fruiting  brush." 

and  even  the  removal  of  a  few  larger  branches,  in  case  the  framework 
is  crowded.  A  word  of  caution  is  necessary  at  this  point.  Since  the 
prune  tree  is  very  susceptible  to  sunburn,  the  best  of  judgment  must 
be  exercised  in  the  thinning  out  of  bearing  trees  as  recommended  above. 
The  Sugar  prune  is  a  variety  which  behaves  somewhat  differently 
from  the  other  sorts  commonly  grown  in  California.  It  has  a  pro- 
nounced tendency  to  make  the  most  of  its  new  growth  on  the  tips  of 
the  previous  season's  shoots,  in  the  same  manner  as  does  the  sweet 
cherry.  It  has  proved  to  be  an  alternate  bearer  in  a  number  of 
different  localities,  and  since  the  wood  is  brittle,  the  branches  fre- 
quently break  during  the  year  of  heavy  production.     In  the  alternate 


Bulletin  3SCJ       PRUNING  BEARING  DECIDUOUS  FRUIT  TREES  47 

years,  then,  when  they  have  a  heavy  set  of  plump  fruit-buds,  the  trees 
should  be  pruned  heavily,  new  shoots  cut  back  especially  to  prevent 
the  formation  of  long,  pole-like  branches,  and  the  fruiting  wood 
thinned  out.  Thinning  of  the  fruit  itself  may  possibly  tend  to  correct 
this  alternating  habit.  In  the  off-year,  when  the  set  of  fruit-buds  is 
rather  light,  comparatively  little  pruning,  especially  in  the  way  of 
limiting  fruit-buds,  should  be  done. 

Quinces. — The  fruit  of  the  quince  is  borne  terminally  on  com- 
paratively long  current  season's  shoots,  arising  from  lateral  and 
terminal  buds  on  one-year  wood.  Since  fruit-buds  are  produced  only 
on  one-year  wood,  attention  must  be  given  to  the  stimulation  of  such 
amounts  of  vegetative  growth  that  the  fruiting  wood  will  be  renewed 
annually.  Experience  has  shown,  however,  that  heavy  production  can 
generally  be  secured  without  a  severe  pruning.  In  fact,  quinces  some- 
times continue  to  bear  good  crops  of  large-sized  fruit  when  very  little 
pruning  is  practiced.  It  seems  best,  nevertheless,  to  give  a  pruning 
which  will  stimulate  from  10  to  24  inches  of  new  growth  each  year  on 
young,  and  from  9  to  18  inches  on  older,  quince  trees.  The  pruning 
should  consist  mainly  of  a  thinning  out  and  heading  back  to  laterals. 
Occasionally,  however,  it  may  be  necessary  to  prune  more  severely  in 
order  to  induce  sufficient  new  growth. 


ACKNOWLEDGMENTS 

The  writer  wishes  to  express  his  appreciation  to  the  following : 

Drs.  E.  J.  Kraus,  W.  L.  Howard,  and  W.  H.  Chandler  for  many 
helpful  suggestions  and  criticisms  in  the  preparation  of  the  manuscript. 

Professor  G.  L.  Philp  and  Mr.  C.  L.  Austin  for  help  in  the  field 
experiments. 

Miss  Edna  Russ  for  her  help  in  the  preparation  of  the  illustrations. 


